The invention relates to a process for the hydroformylation of olefins to produce aldehydes.
It is often desirable to feed two or more olefins at the same hydroformylation facility. In some cases, both olefins are fed to the same reactor. This process, commonly referred to as a “co-feed” process, allows capital savings compared to having separate, complete production trains for each olefin. The co-feed process shares a hydroformylation reactor and product-catalyst separation equipment, and then downstream refining separates the products for further processing. Examples of this process are disclosed in EP 0 052 999, GB 1,120,277, WO 1980/001691, U.S. Pat. No. 4,262,142, Ex. 13 of U.S. Pat. No. 4,400,547 and U.S. Pat. No. 5,312,996.
Inherent to co-feed operation are problems, compared to operations using 2 separate reactor trains, with balancing the reactors with variable feed rates, such as when one feed supply is reduced, and maintaining product isomer ratios. In the first case, a reduction in the amount of the more highly reactive olefin, e.g., ethylene, greatly impacts heat generation, which may make the reactors unstable. Conversely, a reduction in the amount of the less reactive olefin feed will give a first reactor enriched with highly reactive olefin and the reactor coolers may not be able to maintain steady state operation. Changes in feed composition may also impact reactor stability and catalyst performance. For example, an inhibitor in one feed will impact the performance for the entire production system.
Another problem with co-feed operation, compared to operations using 2 separate reactor trains, is that the reactor volume occupied by the product of the more reactive olefin is not productive, and the extra time the product spends in the reactor encourages side reactions such as heavies formation and ligand degradation. Sudden changes in feed quality or availability can generate very extreme catalyst concentrations that may impact overall plant stability.
It is well known that the ratio of linear and branched aldehyde isomer products, commonly referred to as the N:I ratio, is dependent on a number of factors including ligand identity and concentration, usually defined as the ligand-to-rhodium ratio, temperature, and CO and H2 partial pressures. In a co-feed system, these conditions are the same for both reacting olefins, although the desired N:I product ratio for the two products may differ greatly, so that the conditions are a compromise rather than what is optimal for each product.
Based on these concerns, it is common practice to build separate production trains for each olefin despite the additional capital cost. It would be desirable to have a multi-reaction-train hydroformylation process that could operate using a common product-catalyst separation zone, e.g., a vaporizer, as this would result in capital cost savings yet exhibit robust operational stability.